I have a BB Bold 9700 and that also was starting to slow down down and there was connection issues.
I contected it to the BB Desktop software on my computer and it did a self check for any available updates. Mine came back with a OS update which took half an hour to install but it works brand new now. Everything is automatically backed up for you and the OS upgraded to a later version.
If you can't upgrade the OS on your to OS7 then you may have installed a app on there that is taking up to much system memory. I had this with BB protect app. Soon as I uninstalled it went back to normal.
Hope this all helps..:)
Traa Dy Liooar